The effectiveness of allergen immunotherapy (AIT) is often compromised by the use of high doses of allergens for treatment, which can lead to severe systemic reactions and the inconvenience and discomfort of frequent dosing (Kemp, S. F., Immunol Allergy Clin North Am, 2000, 20:571). It has been suggested that the utilization of an adjuvant in conjunction with an allergen vaccine might enhance both the safety and the effectiveness of AIT (Mohapatra, S. S. and San Juan, H. Immunol Allergy Clin North Am, 2000, 20:625-642). Two approaches are under investigation. The first is coimmunization with a mixture of antigen(s) and bacterial DNA or immunostimulatory oligodeoxynucleotides (ODNs), which contain CpG motifs (Horner, A. A. et al., J. Allergy Clin Immunol, 2000, 106:349-356) and elicit a protective TH1 response (Roman, M. et al., Nat Med, 1997, 3:849-854). The potential of CpG-containing ODNs as adjuvants in AIT is under intense investigation; however, it has been reported that the immunostimulatory activity of these ODNs might be blocked by certain non-CpG motifs (Krieg, A. M. et al., Proc Natl Acad Sci USA, 1998, 95:12631-12636; Hacker, H. et al., EMBO J, 1998, 17:6230-6240). In addition, these ODNs might not suppress established allergic responses (Peng, Z. et al., Int Immunol, 2001, 13:3-11). In a second approach, the potential of plasmid DNA (pDNA)-encoding cytokine(s) as genetic adjuvants has been examined, with varying levels of success, for modulating the immune response stimulated by administered antigen vaccines (Pasquini, S. et al., Immunol Cell Biol, 1997, 75:397-401).
Cytokines interferon-γ (IFN-γ) and interleukin-12 (IL-12) are known to mediate T-cell differentiation toward a TH1-like phenotype (Boehm, U. et al., Annu Rev Immunol, 1997, 15:749-795). Despite numerous studies in which pure or recombinant IFN-γ and IL-12 were used, their in vivo use has been limited by the short half-life of these molecules and the associated severe adverse effects (Mohapatra, S. S., Science, 1995, 269:1499). Mucosal IFN-γ gene transfer has earlier been shown to inhibit both antigen- and TH2 cell-induced pulmonary eosinophilia and airway hyper-reactivity (Li, X. M. et al., J. Immunol., 1996, 157:3116-3219). Vaccinia virus-mediated IL-12 gene transfer to the mouse airway abrogated airway eosinophilia and IgE synthesis (Hogan, S. P. et al., Eur. J. Immunol., 1998, 28:413-423). However, the direct effects of these cytokine plasmids as genetic adjuvants in the allergen vaccines used for AIT have not been addressed.
In a previous study, a combination of allergen and IFN-γ effectively redirected allergen-specific T-cell cytokine production toward elevated IFN-γ production in human PBMC cultures (Parronchi, P. et al., Eur J Immunol, 1996, 26:697-703). In a murine model of Kentucky blue grass (KBG) allergy, parenteral administration of 1 mg of recombinant allergen induced effective immune deviation (Cao, Y. et al., Immunology, 1997, 90:46-51). Cytokine gene transfer studies have been carried out (Li, X. M. et al., J. Immunol., 1996, 157:3116-3219; Hogan, S. P. et al., Eur. J. Immunol., 1998, 28:413-423).
It would be advantageous to have the capability to mediate T-cell differentiation toward a TH1-like phenotype using IFN-γ and/or IL-12, thereby enhancing the efficacy of allergen vaccines, without limitation by the short half-life of these molecules and the associated severe adverse effects.